The injection pipeline and the production pipeline in this case have in each case a starting section, which extends partially above-ground, and an active section which is connected to the starting section and extends inside the deposit. During a heating-up phase, the injection pipeline and the production pipeline can be exposed to admission of superheated steam. During a production phase, the injection pipeline can be exposed to admission of superheated steam. Such a device for the extraction of hydrocarbonaceous substances from an underground deposit results for example from “Steam-Injection Strategy and Energetics of Steam-Assisted Gravity Drainage” by I. D. Gates, 2005, SPE International Thermal Operations and Heavy Oil Symposium, Calgary, Canada, 1.-3. November 2005.
According to current estimates, large parts of the worldwide oil reserves exist in the form of so-called oil sands. Oil sand is typically a mixture of clay, sand, water and bitumen. The bitumen can be converted by further process steps into synthetic crude oil. Oil sand deposits are currently preferably extracted in open-cut mining. Oil sand deposits which are located in deeper layers of the earth, however, are extracted with in-situ methods, such as with the SAGD (Steam Assisted Gravity Drainage) method.
In the case of the SAGD method, the bitumen which is present in a deposit is heated by means of superheated steam. In this way, its viscosity is reduced. The bitumen which is liquefied in such a way is extracted from the deposit and supplied to further process steps. Synthetic crude oil can be produced from the bitumen which is extracted from the underground deposit.
For the extraction of oil sand deposits with an in-situ method, pipelines are typically first of all laid inside the deposit. Two pipes which are arranged essentially parallel to each other and extend horizontally are frequently arranged inside the deposit. Such pipes typically have a distance of 5 to 10 m from each other in the vertical direction and have a length of between 500 and 1000 m. At the start of the extraction, the deposit first has to be heated in order to reduce the viscosity of the bitumen which is present in the oil sand, and it is then able to be extracted in liquefied form. For heating the deposit, the two pipes which extend inside the deposit are typically exposed to admission of superheated steam. After the termination of the approximately 3-month heating-up phase, in the subsequent production phase only the pipe which lies geodetically higher is exposed to admission of superheated steam. The superheated steam which is injected into this pipe leads on the one hand to further liquefaction of the bitumen which is present in the deposit, and on the other hand leads to a positive pressure in the deposit. Driven by this positive pressure, liquefied bitumen can be transported in the meantime through the second pipeline to the earth's surface.
The currently applied SAGD method has diverse technical problems. On the one hand, superheated steam can escape from the actual area of the deposit via passages which exist in the area of the deposit or which are attributable to further geological features inside the deposit, for example porous rock layers. The superheated steam which escapes in this way is lost for extraction of the bitumen.
Furthermore, the quantity of heat, which can be introduced into the deposit by means of superheated steam, is limited for the following reasons. The quantity of heat which can be introduced into the deposit is determined to a substantial degree by the maximum permissible pressure with which superheated steam can be injected into the deposit. Oil sand deposits are typically not located at very great depths so that as a result of an excessive pressure build-up inside the deposit earth displacements on the surface can occur. Furthermore, large amounts of water are required for the extraction of bitumen from oil sand deposits by means of the SAGD method. The required amount of water is measured based on the so-called “steam to oil ratio” (SOR). Strict environmental requirements in the extraction fields require an SOR which is as low as possible in order to take into consideration the conserving of ground water supplies.
The extraction duration of an oil sand deposit, which is extracted using two pipes with the typical previously mentioned dimensions, is typically within the range of between 3 and 10 years. Over this time, the deposit is continuously heated with superheated steam. On account of the thermal conductivity of the soil, the heat which is introduced into the deposit reaches in the course of time ever greater distances from the point at which superheated steam is introduced into the deposit. The intake area of the production pipe, via which liquefied bitumen is transported to the surface, is spatially limited. Heat, which reaches beyond the limits for the intake area of the production pipe, is lost for the production of bitumen. This phenomenon leads not only to a deterioration of the “steam to oil ratio” but also to a poor overall energy balance of the deposit in question.